1. Field of Invention
The present invention relates to a mobile terminal and method of indentifying SIM card thereof, and more specifically to a mobile terminal supporting at least two SIM cards and method of indentifying the SIM cards thereof.
2. Description of Related Arts
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
The SIM (Subscriber Identity Module) card for mobile terminal, such as mobile phone, stores system original data inputted by the manufacturer, mobile phone information, information inputted by user, data relative to the mobile telecommunication network, and relevant service code, which are necessary to ensure the function of the mobile terminal.
SIM card is a chip card with a micro CPU, which has 5 modules inside thereof: a micro CPU (8 digit), a program ROM (3˜8 kbit), a working RAM (6˜16 kbit), a data EEPROM (16˜256 kbit), and a serial communication unit. The 5 modules are sealed to the copper interface of the SIM card, and packaged like ordinary IC card. The SIM card connects the logical circuit thereof and mobile terminal via the copper interface of the SIM card. The SIM card has 8 pins, usually 6 of which are needed to connect with the mobile terminal.
The operating voltage of the SIM launched before 1998 is 5V. The SIM cards afterwards are compatible with 3V and 5V or compatible with 1.8V and 3V. The SIM card must cooperate with the mobile phone. That is to say, the power supply for SIM card of mobile phone must match the operating voltage of the SIM card. Otherwise, the mobile phone cannot indentify the SIM card, that is to say, the mobile phone cannot provide communication function. Besides, when the power supply of mobile phone is higher than the operating voltage of the SIM card, the SIM card may be burned. In order to solve this problem, a U.S. Pat. No. 6,381,477B1 discloses a method for protecting a circuit module in a communication device includes steps of: first detecting whether a circuit module is present in the communication device, measuring a supply voltage to the communication device, comparing the supply voltage to a predetermined threshold voltage, when the supply voltage is below the threshold, supplying normal functionality to the phone and returning to the comparing step, when the supply voltage is above the threshold, powering down a connection to the SIM card to limit functionality of the communication device. However, this method has drawbacks in compatibility and adaptability. For example, when the SIM card is compatible to two different operating voltages, this method can not assure that the SIM card work in the best operating voltage.